1. Field of the Invention
This invention is related to semiconductor processing equipment. More specifically, this invention relates to a processing chamber for semiconductor processing and methods for confining plasma gas within a processing zone of the processing chamber.
2. Background of the Related Art
Semiconductor integrated circuits are fabricated with multiple layers of semiconductive, insulating, and conductive materials, as well as additional layers providing functions such as bonding, a migration barrier, and an ohmic contact. Thin films of these various materials are deposited or formed in a number of ways, the most common of which in modern processing are physical vapor deposition (PVD), also known as sputtering, and chemical vapor deposition (CVD).
In CVD, a substrate, for example a silicon substrate, which may already have patterned layers of silicon or other materials formed thereon, is exposed to a precursor gas which reacts at the surface of the substrate and deposits a product of the reaction, e.g. TiN, Al, etc., on the substrate to grow a film thereon. This surface reaction can be activated in at least two different ways. In a thermal process, the substrate is heated to a sufficiently high temperature to provide the activation energy necessary to cause the precursor gas adjacent to the substrate to react and deposit a layer on the substrate. In a plasma-enhanced CVD process (PECVD), the precursor gas is subjected to a sufficiently high electromagnetic field which excites the precursor gas into energetic states, such as ions or radicals, which react on the substrate surface to form the desired material.
One type of CVD chamber commercially available from Applied Materials, Inc., of Santa Clara, Calif., is known as a CVD DxZ Chamber and is illustrated in the cross-sectional side view of FIG. 1. The CVD chamber 30 includes a pedestal 32 having a supporting surface 34 on which a substrate 36 is supported for chemical vapor deposition of a desired material thereon. Positioning the substrate 36 on the supporting surface is facilitated by vertically movable lift pins 38.
A gas delivery assembly 31 is disposed on a lid rim 66 at an upper end of the chamber body 72 and includes a gas distribution faceplate 40, often referred to as a showerhead, and a gas-feed cover plate 46, or temperature control plate, disposed on the showerhead 40 and in thermal communication therewith. An annular flange 47, (shown in FIG. 2) which is an integral component of the showerhead 40, is disposed on an isolator 64 to support the gas delivery assembly 31. A plurality of holes 42 arc formed in the showerhead 40 and are adapted to accommodate gas flow therethrough into the process region 56. The gas is provided to the showerhead 40 by a central gas inlet 44 formed in the gas-feed cover plate 46. The gas-feed cover plate 46 also includes a multi-turn cooling/heating channel 33 to accommodate the flow of water or other fluid therethrough during processing in order to maintain the gas delivery assembly 31 at a desired temperature. The gas delivery assembly 31 may be cooled or heated depending on the particular chemicals being delivered through the central gas inlet 44. In operation, the temperature controlled gas delivery assembly 31 is intended to contribute to uniform deposition and prevents gas decomposition, deposition, or condensation within the gas distribution system upstream from the process zone.
In addition to assisting in gas delivery into the chamber 30, the showerhead 40 also acts as an electrode. During processing, a power source 94 (FIG. 1) supplies power to the showerhead 40 to facilitate the generation of a plasma. The power source 94 may be DC or RF.
In operation, a substrate 36 is positioned on the pedestal 32 through cooperation of a robot (not shown) and the lift pins 38. The pedestal 32 then raises the substrate 36 into close opposition to the showerhead 40. Process gas is then injected into the chamber 30 through the central gas inlet 44 in the gas-feed cover plate 46 to the back of the showerhead 40. The process gas then passes through the holes 42 and into the processing region 56 and towards the substrate 36, as indicated by the arrows. Upon reaching the substrate 36, the process gases react with the upper surface thereof. Subsequently, the process gas byproducts flow radially outwardly across the edge of the substrate 36, into a pumping channel 60 and are then exhausted from the chamber 30 by a vacuum system 82.
However, PECVD processes have demonstrated some problems with deposition uniformity, reproducibility and reliability. It is believed that the problems originate from temperature gradients over various chamber component surfaces as well as from extraneous metal depositions on the chamber surfaces affecting the plasma and producing excess particles within the chamber. With regard to extraneous metal deposition, it is believed that the deposition occurs in two different areas, an area at the top of the pedestal 32 outside of the substrate 36 and an area in and around the pumping channel 60.
One problem associated with conventional CVD chambers is the temperature non-uniformity over the surface of the showerhead 40. As a result of the power applied to the showerhead 40 by the power source 94, the temperature of the showerhead 40 increases over time until reaching thermal stabilization which is determined, in part, by the thermal exchange between the showerhead 40 and the plasma, and the showerhead 40 and the gas-feed cover plate 46. While acceptable results were achieved for 200 mm chambers, thermal stability and uniformity worsened as the chambers were scaled up to accommodate larger substrates, such as 300 mm substrates. Because the uniformity of deposition is at least partially dependent on temperature, the resultant temperature gradient over the surface of the showerhead 40 produces non-uniform deposition on the substrate.
One cause of temperature non-uniformity throughout the bulk of the showerhead 40, is design features of conventional lid assemblies provided to accommodate thermal stresses during operation. For example, referring to FIG. 2, the gas-feed cover plate 46 is shown disposed on the showerhead 40. The outer annular wall 35 of the gas-feed cover plate 46 is in facing relation to the inner annular wall 37 of the showerhead 40 to define a gap 39 therebetween. While preferably minimized or nonexistent at room temperature, the gap 39 is widened during processing due to the differing coefficients of expansion of the gas-feed cover plate 46 and the showerhead 40 which causes the showerhead 40 to expand to a greater degree. As a result, the gap 39 acts to insulate the gas-feed cover plate 46 and the showerhead 40 from one another, thereby inhibiting thermal exchange.
Temperature non-uniformity over the surface of the showerhead is also a result of the limitation of space which require that the dimensions of the gas delivery assembly 31 be minimized in order to reduced the cost of manufacturing and operation. In order to ensure the desired heating or cooling of the gas delivery assembly 31, the gas-feed cover plate 46 requires sufficiently large dimensions to accommodate the cooling channel 33. As a result of the large size of the gas-feed cover plate 46, the showerhead thickness is minimized to achieve a compact gas delivery assembly 31. In scaling up to accommodate larger substrates, it was initially believed that the ratio of dimensions could be maintained without a loss of deposition uniformity. However, 1:1 scale-up results in thermal non-uniformity over the surface of the showerhead 40. In particular, the center of the showerhead 40 experiences considerably higher temperatures relative to the edge, thereby resulting in a temperature gradient from center to edge. As a result of the temperature gradient, deposition on the substrate is non-uniform which can lead to defective devices.
FIG. 3 is a graphical representation of the temperature profile for a conventional showerhead which was scaled up to accommodate 300 mm substrates. The scale up ratios were approximately 1:1, meaning that the ratios of dimensions for the components were held equal. The applied power to the showerhead was about 920 W and the thermal contact resistance, Rc, was about 5xc3x9710xe2x88x924 m2K/W where Rc is defined as the ratio of the change in temperature between two surfaces and the heat flux across the surfaces (xcex94T/q). Three curves 41, 43, 45 are shown in FIG. 3 representing the temperature fluctuations for the center, mid-portion, and edge, respectively, of the showerhead 40 for six substrates. The substrates are numbered S1-S6 and the process cycle for each corresponds to the upward sloping portion of the curves 41, 43, 45. The temperature gradient for the center, xcex94T1, for the six substrates is about 13xc2x0 C. and the temperature uniformity spread, xcex94T2, is about 5xc2x0 C., where xcex94T1 is defined as the change in temperature at the center of the showerhead 40 from the sixth substrate to the first ((Tcenter)6thxe2x88x92(Tcenter)1st) and xcex94T2 is defined as the difference of the center-to-edge temperature gradient between the sixth substrate and the first substrate ((Tcenterxe2x88x92Tedge)6thxe2x88x92(Tcenterxe2x88x92Tedge)1st, shown in FIG. 3 as xcex94T4xe2x88x9266 T3). Further, the difference in temperature xcex94T3 between the center and the edge for the first substrate, S1, is about 11.0xc2x0 C. and the difference in temperature xcex94T4 between the center and the edge for the sixth substrate, S6, is about 16xc2x0 C. Thus, the showerhead 40 exhibited large center-to-edge temperature gradients during processing which resulted in non-uniform deposition on substrates. In addition, FIG. 3 shows no tendency of stabilization at a steady state. Thus, the temperatures at each point in the showerhead 40 show significant increases with time as represented by upward sloping curves 41, 43, 45, and the rate of heat transfer from center to edge is also in flux as indicated by xcex94T3 and xcex94T4.
Another problem associated with conventional CVD chambers relates to extraneous metal deposition or buildup. Extraneous metal deposition arises because material, such as TiN, is deposited on chamber surfaces exposed to the process gas along its path from the showerhead 40 to the chamber vacuum system 82. The metal deposits can cause an electrical short between the electrically biased showerhead 40 and grounded chamber components. Material buildup leads to undesirable effects during processing which can result in defective devices. One detrimental effect of material buildup is a reduction in plasma uniformity. Plasma uniformity in the processing region 56 depends on the distance between the powered electrodes and surrounding surfaces and the difference between their respective electrical potentials. When, during a long process run, insulating components disposed in the chamber 30 effectively change from being insulators to being grounded conductors, the location and quality of the plasma will be affected. The distortion of the plasma due to the proximity of an adjacent electrical ground causes non-uniformity in the plasma. During plasma processing, variations in uniformity and intensity of the plasma will affect the surface uniformity of the film produced and reduce the process repeatability.
In addition to affecting the plasma uniformity, deposits within the chamber can also result in arcing. In some cases, the arcing may occur near the substrate. Arcing can create particles and defects on the substrate. Therefore, arcing to the substrate should be avoided and the uniformity of the envelope for the plasma adjacent the surface of the substrate should be held as uniform as possible.
Therefore, there is a need for a CVD chamber that does not possess the problems of temperature non-uniformity, plasma instability and arcing and where the frequency for routine maintenance and cleaning is reduced.
Preferred embodiments of the invention provide a system for processing of substrates in a plasma-enhanced chemical vapor deposition (PECVD) chamber. Embodiments of the present invention include a PECVD system for depositing a film of titanium nitride from a TDMAT precursor. The present invention broadly provides an apparatus for processing substrates that includes a chamber, a gas delivery assembly, a pedestal which supports a substrate, and a plasma system.
In one aspect of the invention, a gas delivery assembly is provided to supply one or more gases to a chamber. The gas delivery assembly generally includes a temperature control plate and a showerhead mounted thereto. Preferably, the interface between the showerhead and temperature control plate is parallel to a radial direction of the gas delivery assembly to accommodate lateral thermal expansion without separation of the showerhead and the temperature control plate. A blocker plate, or baffle plate, may be disposed between the showerhead and temperature control plate to facilitate dispersion of gases delivered thereto.
In another aspect of the invention, a processing chamber includes a chamber body and a lid assembly disposed thereon to define a chamber cavity. A pedestal movably disposed within the chamber cavity is adapted to support a substrate during processing. The lid assembly is supported by the chamber body and includes an isolator ring member and a gas delivery assembly supported thereon. The gas delivery assembly generally includes a temperature control plate and a showerhead mounted thereto. Preferably, the interface between the showerhead and temperature control plate is parallel to a radial direction of the gas delivery assembly to accommodate lateral thermal expansion without separation of the showerhead and the temperature control plate. In one embodiment, the processing chamber further includes one or more chamber inserts and/or liners. The chamber inserts and/or liners are adapted to control plasma uniformity and arcing and are readily removable for cleaning.